Currently, the propylene oxide production is mainly conducted worldwide by means of the hydrochlorin route method and the co-oxidation method. The hydrochlorin route method will be gradually eliminated due to the pollution problem. The co-oxidation method seems hardly to be developed to a further large scale due to the limited use of its byproducts. Therefore, the production of propylene oxide is greatly limited by the above production methods. In recent years, a new route for preparing propylene oxide comes out. According to this new route, propylene is epoxidated with an oxidant H2O2 under the titanium silicate catalysis to become propylene oxide. This route has the advantages such as the mild reaction condition and the environmentally friendly process without pollution, and therefore becomes a new green technology for producing propylene oxide.
CN1671678A discloses an epoxidation method with two fixed bed reactors, wherein the first reactor is an isothermal fixed bed reactor, and the second reactor is a thermal insulation fixed bed reactor. The disadvantage of this method includes the conversion of H2O2 used in the reaction is not completely, and the unreacted H2O2 will decompose in the separation column to produce oxygen, which causes a safety concern and even an explosion when badly managed.
CN1449392A discloses a method for preparing an alkylene oxide with a peroxidized compound. In this method, the alkylene oxide is prepared by reacting an olefin and the peroxidized compound in at least two reactors in series (in each of the reactors, a part of catalyst is loaded) in the presence of catalyst and solvent. According to this method, the peroxidized compound is only supplied to the first reactor, and none of the fresh peroxidized compound is added to the subsequent one or more reactors, to each of which the unconsumed peroxidized compound from the preceding reactor is supplied so as to completely convert H2O2 in the reaction. The reactor used in this method is fixed bed reactor or moving bed reactor. According to this method, at least two reactors are used, preferably three reactors in series. The disadvantages of this method include: if using two reactors at a minimum, the conversion of H2O2 is still not completely; if using more than two reactors in series, the device cost will increase remarkably and the reaction period of multiple reactors in series is long and the uncontrollable factors in the reaction process are overmuch.
Therefore, there is an urgent need in the prior art to develop a process for producing alkylene oxide by olefin epoxidation, which can completely convert H2O2 used in the reaction and has a high selectivity for the target alkylene oxide (e.g. propylene oxide).